Patent GB-190426699-A (GB)
Title: Improvements in Electric Motor Controlling Systems.
Inventor: EASTWOOD ARTHUR CLARKE
Filed: 1904-12-07
Granted: 1905-02-16
Abstract: 26,699. Eastwood, A. C. Dec. 7. Motors, controlling.-Relates to a system of control for motors which require to be frequently and rapidly reversed, as, for example, those employed in connection with reversing roller-tables in iron and steel mills for feeding ingots, billets, or blooms to the rolls, and with reciprocating planers and other metal-working machines. Electromagnetic means are provided for, (1), inserting a bank of resistance in the armature circuit at starting in either direction; (2),successively cutting out sections of the said resistance as the motor speeds up; (3), either short-circuiting the armature through a braking-resistance, Fig. 2, or connecting a braking- resistance in series with the starting-resistance, Figs. 6 and 10, when the motor-circuit is broken at the instant before reversal by the movement of the reversing-controller. Fig. 2 shows the invention applied to a shunt-wound motor adapted to operate at its full or at a constant speed. The apparatus comprises a reversing-controller C with fixed contacts a<1>-a<5> and two sets of movable contacts c<1>-c<5>, and a bank of starting-resistance R in series with the armature A and mains L, L<1>, which is placed in circuit by an electromagnetic switch M and is sectionally cut out by the successive operations of three electromagnetic switches S<1>, S<2>, S<3> connected in parallel across the armature terminals and actuated in order as the voltage applied to their coils increases, the current remaining practically constant. The armature A is short-circuited through a resistance R<4> when the controller is being reversed, by the closing of an electromagnetic switch N, the operating-coil n<2> of which is in shunt with the armature. The switch M remains open until the armature A has come to rest, and, in order to prevent both the switches M, N from being open or closed at the same time, they are coupled together by a centrally-pivoted lever o, Fig. 5. All the switches are provided with retractive springs, and the invention may be similarly applied to a compound-wound motor. In a variable-speed motor, the successive actuation of the switches S<1>, S<2>, S<3>, instead of being automatic as described above, is regulated by the contrcller C. One end of each of the switch coils is connected to an additional contact-finger in the controller adapted to engage with corresponding contact-segments on both sides. In the modification shown in Fig. 6, the speed of the motor is varied by varying the field strength, and at starting the armature A is connected with the mains through a normally-open switch S<7>, the actuating-coil of which is in series with the coils of switches S<8>, S<9> controlling the starting - resistance R. At the instant before reversal, the sections R<5>, R<6>, R<7> of the braking- resistance are connected in series with the resistance R, and, as the armature slows down, the sections R<5>, R<6>, R<7> are successively short-circuited by the closing of spring-controlled switches S', S<5>, S<6>, the coils of which are arranged either in multiple or in series across the armature terminals, or, by providing the controller with additional contacts, the motor may be run at any desired speed. The switches S<6>, S<7> are joined by a yoke p so that they may both be in their ocen or closed positions at the same time. The starting-resistance is then gradually cut out as the motor is accelerated in a reverse direction, and, finally, the field f is weakened by the switching-in of one of two rheostats r, r'. The rheostats are normally short-circuited by means of the switches S<10>, S<11>, which are opened by the bridging of contacts S' on the closure of the switch S<9>. Two rheostats are employed for the purpose of allowing the motor to be accelerated to different speeds after successive reversals. In the case of a series-wound motor, in order to ensure the switches S<4>, S<5>, S<6> remaining open when the controller is reversed, they are provided with auxiliary windings connected in series with one another aud in shunt across the mains. The terminals of the auxiliary windings are carried to two fingers of the controller, the corresponding contact - segments being so arranged that contact is made before the main circuit of the motor is closed and is broken when the motor has been moved to its full 'on' position. The contacts on the reversing-controller may be so arranged as to operate the motor with any number of starting-resistance sections in series. In a system for the automatic control of a compound-wound motor, the hand-operated controller is dispensed with, the windings of the switches S<4>, S<5>, S<6> are joined in series across the armature terminals, and the starting and resistance switches S<7>, S<8>, &c. are connected in multiple from the resistance R to a common lead, which runs to the negative pole of the main switch B and is opened and closed by a switch operated automatically by a float &c. Fig. 10 shows the application of the invention to a series-wound motor controlled by reversing-switches S<13>-S<16>, the coils of which are supplied with current through a hand-operated controller Q. The ends of the pairs of coils S<13>, S<15> and S<14> S's are connected together and to the controller segments q<1>, q<2>, their other extremities communicating with the positive main. The coils of the starting-resistance switches S<8>, S<12> are respectively connected to the controller through auxiliary switches r<3>, r<4>, r<5> situated thereon. A coil s<7> in shunt with the armature A operates a movable blade s<8>, which acts to prevent closure of the starting-switch S<7>. Locking-bars o extend between the switches S<13>, S<14> and S<15> S<16>, so that one switch only of each pair can be in a closed position at the same time. On moving the controller handle q from the position x-x to the position y-y, the coils of the switches S", S<16>, S<7> will be open-circuited, and the switches S<13>, S<15> will be closed. Current from the supply mains then flows to the armature through the braking- resistance R<5>, as well as through the starting- resistance R, the switch S<7> being prevented from closing until the armature counter-electromotive force through the coil s<7> has fallen to zero.